11-1
11 BPDU Tunneling Configuration
When configuring BPDU tunneling, go to these sections for information you are interested in:
z Introduction to BPDU Tunneling
z Configuring BPDU Tunneling
z BPDU Tunneling Configuration Examples
Introduction to BPDU Tunneling
As a Layer 2 tunneling technology, BPDU tunneling enables Layer 2 protocol packets from
geographically dispersed customer networks to be transparently transmitted over specific channels
across a service provider network.
Background
Customers usually use dedicated lines in a service provider network to build their own Layer 2
networks. As a result, very often, a customer network is broken down into parts located at different
sides of the service provider network. As shown in
Figure 11-1, User A has two devices: CE 1 and CE 2,
both of which belong to VLAN 100. User A’s network is divided into network 1 and network 2, which are
connected by the service provider network. When Layer 2 protocol packets cannot be transparently
transmitted in the service provider network, User A’s network cannot implement independent Layer 2
protocol calculation (for example, STP spanning tree calculation). In this case, the Layer 2 protocol
calculation in User A’s network is mixed with that in the service provider network.
Figure 11-1 BPDU tunneling application scenario
ISP network
User A network 1
VLAN 100
User A network 2
VLAN 100
CE 1 CE 2
PE 1 PE 2
With BPDU tunneling, Layer 2 protocol packets from customer networks can be transparently
transmitted in the service provider network:
2) After receiving a Layer 2 protocol packet from User A network 1, PE 1 in the service provider
network encapsulates the packet, replaces its destination MAC address with a specific multicast
MAC address, and then forwards the packet in the service provider network;
3) The encapsulated Layer 2 protocol packet (called bridge protocol data unit, BPDU) is forwarded to
PE 2 at the other end of the service provider network, which decapsulates the packet, restores the
original destination MAC address of the packet, and then sends the packet to User A network 2.
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